The highly invasive lionfish is easily available through aquarium and internet sales and represents a potential threat for California waters.

In the film "Finding Nemo," a plucky clownfish escapes an aquarium tank thanks to some sage advice: "All drains lead to the ocean."

But in real life, flushing Nemo wouldn't end happily. Aquarium species are some of the hardiest fish and plants in the world, and tank owners and importers who dump unwanted marine life are introducing tough, non-native species to California waters, says a new report on the state's aquarium trade.

"Globally, the aquarium trade has contributed a third of the world's worst aquatic and invasive species," said Sue Williams, lead author of the report and an evolution and ecology professor at the University of California, Davis Bodega Marine Laboratory. That includes both marine and freshwater species, she said.

In California, 13 species found only in dentist's offices or other fish tanks have escaped to the state's marine waters, presumably due to release by aquarium owners or importers.

"We have no data on how many aquarists dump their organisms into natural waters, we only know that they do so because these are species that could only come through the aquarium trade," Williams told OurAmazingPlanet. A survey of aquarists (people who keep fish) in Texas, cited in the UC Davis report, found 20 to 69 percent of them admitted dumping, she said.

The report is one of six that the UC Davis Bodega Marine Laboratory prepared for the state, each exploring a different vector, or pathway, through which invasive species can enter California ocean waters. The other pathways include aquaculture, live seafood, live bait, fishing vessels and recreation vessels.

Every year, San Francisco and Los Angeles ports see more than 11 million non-native, ornamental marine individuals - such as tropical fish, seaweed and snails - bound for aquariums, representing at least 102 species, Williams and her colleagues discovered.

One of the worst introduced species is a killer algae. Though actually a type of seaweed, the species Caulerpaearned its nickname when it infected two lagoons in Southern California in 2000, costing more than $6 million to eradicate.

Though most imported marine life comes from Indonesia and the Philippines, where ocean temperatures are warm, the report found 34 species could survive in California's chilly bays. "[Aquarium species] are highly likely to survive in the wild, because they have to be so tough to survive the trade," Williams said. Some can even survive a trip down the toilet, she said.

One potential invader is the lionfish, a venomous predator that gulps down smaller fish. In Florida and the Bahamas, authorities have organized fishing derbies to counter lionfish attacks on local reef fish.

Williams said a little outreach could prevent the lionfish and other predators from gaining a toehold in California. "[The aquarium trade] might be the vector that is most easily managed, because it really just requires public awareness."

Williams recommends aquarium owners who want to toss live fish call the pet shop that sold the fish, trade or sell fish on eBay (where it's legal to do so) or ask the California Department of Fish and Wildlife for advice. If all else fails, - or "if they're queasy about getting rid of it," William's euphemism for killing - she advises to remember it's for a greater good.

"When these species are released, they can do some major ecological and economic harm," she said.